Archive for August 15th, 2009

NiMH Cell Comparisons

I collected some loose cells and pulled some cells from the packs to see how they compared individually.

These are discharging at 500 mA, rather than 1 A, mostly because there were fewer tests and I could run ’em overnight. Other than the Tenergy RTU cell, they’re all old and wearing out…

Single Cell Comparison - Aug 2009

Single Cell Comparison - Aug 2009

The green line is a new Tenergy RTU 2.3 Ah cell; it has a higher voltage, but still isn’t delivering anything close to its rating even at a load only slightly higer than C/5. I have three packs of those that will be cycling through the amateur radios on the bikes, but I don’t like the relatively low capacity. I’ll run these eight cells through the fast charger and do some rundown tests to see if they improve; I have my doubts.

The black line comes from an old batteries.com 2.5 Ah cell. It has the highest capacity of the group, but a rather low voltage. I’ll start cycling those through the blinky lights on the bikes.

The red line is a Tenergy 2.6 Ah cell. I think these are a year or two old, so they’re not faring well at all. OK voltage, but very low capacity. I think the batteries.com cells will work better in the lights, as they have 50% more capacity at a slightly lower voltage.

The blue line is an ancient Lenmar 2.0 Ah cell. As a fraction of its rated capacity, it’s doing OK, but the low voltage is a dealbreaker. Scrap.

Given the poor results from the old & new Tenergy cells, I’m not sure quite what to do. The advertised ratings are obviously optimistic, shipping charges pretty much wipe out any incentive to sample a batch of new cells, and cells get reformulated often enough that old tests you find on the web (this one included!) are useless.

Grumble…

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